1. Technical Field
The present invention generally relates to methods for treating the side effects of chemotherapy and radiation therapy in mammals.
2. Description of the Related Art
Generally, normal cells in a mammal grow and divide in an orderly and controlled manner. Cancer is a disease where cells become abnormal (cancerous cells) and begin to multiply without control to develop into an extra mass of tissue called a tumor. These cancerous cells can invade nearby tissue and spread through the blood stream and lymphatic system to other parts of the body.
Presently, the four primary types of cancer treatments are immunotherapy, surgery, radiation therapy, and chemotherapy. These cancer treatments may be applied alone or in conjunction with one another. Accordingly, a cancer patient may undergo one or more treatments at a time. A single treatment could span a period of time with therapies delivered at various time intervals. Immunotherapy attempts to stimulate or restore the ability of the immune system to fight the disease. It may also be used to lessen immune-system-related side effects that may be caused by some cancer treatments. Surgery seeks to directly remove the tumor from the body.
Radiation therapy, also known as radiotherapy, uses high-energy radiation from x-rays, gamma rays, neutrons, and other sources to kill cancer cells and shrink tumors by damaging the cells' genetic material. While cancerous cells are damaged permanently and eventually die, normal cells that are damaged in radiation therapy are able to repair themselves. Side effects that can occur during radiation therapy include skin irritation and hair loss in the area being treated, as well as damage to the bone marrow.
Chemotherapy uses cytotoxic drugs, alone or in combination, to destroy cancer cells. As in radiation therapy, cancer cells can be damaged and eventually die, but healthy cells affected in the process can repair themselves after chemotherapy. Cytotoxic drugs work by interfering with the ability of a growing cell to divide and reproduce itself. Thus, in addition to cancerous cells, other normal fast-dividing, growing cells can also be affected. For example, there can be an effect on blood cells formed in the bone marrow, causing bone marrow suppression. There can also be an effect on cells in, for example, the digestive tract, in the lining of the mouth, and in the reproductive system, causing diarrhea and mouth soreness; there can also be an effect on hair follicles, causing hair loss.
Bone marrow suppression is one of the many side effects of chemotherapy and radiation therapy. It results in reduced blood cell production, including red blood cells, white blood cells, and platelets. Consequently, a patient can experience fatigue from anemia, become more susceptible to infections, from leukopenia, and bruise easily and bleed more when getting a cut, from thrombocytopenia. Drugs are typically used to counter the bone marrow suppression side effect. For example, Epogen® (epoietin α) has been used to counter the side effect of anemia in cancer chemotherapy, and WinRho® SDF (Rho (D) immune globulin) has been used to counter the side effects of thrombocytopenia.
Prevention of, or protection from, the side effects of chemotherapy and radiation therapy would be a great benefit to cancer patients. The many previous efforts to reduce these side effects have been largely unsuccessful. For life-threatening side effects, efforts have concentrated on altering the dose and schedules of the chemotherapeutic and radiotherapeutic agents to reduce the side effects. Other options are becoming available, such as the use of granulocyte colony stimulating factor (G-CSF), granulocyte-macrophage-CSF (GM-CSF), epidermal growth factor (EGF), interleukin 11 (il-11), erythropoietin, thrombopoietin, megakaryocyte development and growth factor, pixykines, stem cell factor, FLT-ligand, as well as interleukins 1, 3, 6, and 7, to increase the number of normal cells in various tissues before the start of chemoradiotherapy. The mechanisms of protection by these factors, while not fully understood, are most likely associated with an increase in the number of normal critical target cells before treatment with cytotoxic agents or radiation therapy, and not associated with increased survival of cells following chemoradiotherapy.
Generally, neutrophils, also called polymorphonuclear leukocytes, are the most numerous of the blood cells known as granulocytes. Neutrophils are the largest cell population involved in acute inflammatory response. They are thus an important component of natural immunity, responding quickly to chemotactic stimuli. Neutrophils destroy foreign particles such as bacteria by enveloping and digesting them, a process called phagocytosis. Neutrophils may increase in response to bacterial infection. When many neutrophils are needed, they are released from the bone marrow as immature cells, called bands or stab cells. Neutropenia is a hematological disorder characterized by an abnormally low number of neutrophil granulocytes. Therefore, patients with neutropenia are more susceptible to bacterial infections, and these conditions may become life-threatening.
Neutropenia may occur secondary to another condition such as cancer or Acquired Immunodeficiency Syndrome (AIDS). Neutropenia may also occur secondary to an event such as a drug therapy. Thus, neutropenia may result from physiological disorders that directly affect the immune system. For example, diminished neutrophil production will result when leukemia, myeloma, lymphoma or a metastatic solid tumor such as, for example, breast or prostate cancer, infiltrate and replace bone marrow. Transient neutropenia is often associated with viral infections. Chronic neutropenia is often associated with immunodeficiency resulting from a viral infection, for example, AIDS resulting from infection with Human Immunodeficiency Virus (HIV). Autoimmune neutropenia may be associated with circulating anti-neutrophil antibodies.
A much more common cause of neutropenia is as a side effect of drug therapy, particularly chemotherapy and radiation therapy for cancer and bone marrow transplantation associated with cancer therapy. Neutropenia secondary to drug therapy can thus be subdivided into two groups. The first involves immune-mediated neutropenia that may arise from drugs that act as haptens to stimulate antibody formation. Acute hypersensitivity reactions such as those caused by diphenylhydantoin and phenobarbital may last a few days. However, chronic hypersensitivity reactions may last for months or years.
The second area of drug-induced neutropenia involves the severe neutropenia that predictably occurs after large doses of cytoreductive cancer drugs or ionizing radiation therapy. These cytotoxic therapies induce neutropenia because of the proliferative nature of neutrophil precursor cells and the normal rapid turnover rate of circulating neutrophils. The risk of neutropenia secondary to cancer chemotherapy or radiotherapy depends on such factors as the type and stage of the cancer and the type, the dosage and the schedule of cancer treatment.
Therapy that presently exists for raising neutrophil levels consists primarily of filgrastim (Neupogen®) and more recently, pegfilgrastim (Neulasta®), a longer acting derivative of filgrastim. Filgrastim is a recombinant version of a human protein, G-CSF, that selectively stimulates the production of white blood cells. G-CSF is currently the drug of choice for neutropenia. Since both of these drugs are recombinant proteins they are not active orally and must be administered by injection. In addition, protein-based drugs are often subject to rapid metabolism.
Despite advances in the fields of chemotherapy and radiation therapy, prior art drugs and methods have proven to be of limited utility in minimizing side effects resulting from chemotherapy and radiation therapy such as chemotherapy-induced alopecia, radiation therapy-induced alopecia, chemotherapy-induced thrombocytopenia, radiation therapy-induced thrombocytopenia, chemotherapy-induced leukopenia, radiation therapy-induced leucopenia, chemotherapy-induced neutropenia and radiation therapy-induced neutropenia. Accordingly, it would be desirable to provide an improved method for treating such side effects of chemoradiotherapy in a mammal.